1. Field of the Invention
This invention relates to blood collection and, more particularly, relates to a plastic blood sample collection assembly.
2. Background
Blood samples are routinely taken in evacuated tubes, such as glass VACUTAINER.TM. tubes (Becton, Dickinson and Company). One end of a double-ended needle is inserted into a patient's vein. The other end of the needle then punctures a septum covering the open end of the VACUTAINER.TM. tube so that the vacuum in the tube draws the blood sample through the needle into the tube. Using this technique, a plurality of samples can be taken using a single needle puncture of the skin. Plastic tubes have also been proposed for blood collection. Plastic offers a number of advantages over glass such as lower breakage, less weight in shipment, and easier disposal by incineration.
Blood collected in evacuated tubes often must be clotted prior to clinical examination. It is desirable to form a dense clot as rapidly and completely as possible to facilitate clean separation of the clot from the serum layer by centrifugation. To achieve this end, both plastic and glass blood collection tubes frequently employ a clot activator. Typical activators are diatomaceous earth and particles of inorganic silicates, or biochemicals such as ellagic acid and thromboplastin. In one line of commercial blood collection tubes, for example, a coating of silicate particles in polyvinylpyrrolidone (PVP, a water soluble polymer) is affixed to the inside of the tube. When blood enters the tube, the PVP dissolves and silicate particles are released to initiate clotting. The PVP enters both the serum and clot.
A problem with particulate activators is that finely divided particles may not pellet completely with the clot and may thus contaminate the serum layer and interfere with certain blood analyses. In addition, particles suspended in the serum may foul automatic blood analysis instruments. On the other hand, soluble biochemical activators can be disadvantageous because these cannot be easily separated from either the serum or blood clot and can interfere with both chemical and hematological assays. In particular, for highly specialized applications, such as blood banking, it is unacceptable to have either soluble activators or particulates in the cell mass of a blood clot because these cells are used in blood typing analyses. For this reason, samples for blood banking are routinely taken in glass tubes and rely on the clot activating property of the glass to induce clotting. There is a need in the art of blood collection for equipment which provides an enhanced rate of blood coagulation without leaving any soluble or particulate material in the serum layer or in the clot on centrifugation, thus avoiding potential interference with clinical tests, and particularly in blood banking procedures. The present invention is directed to fulfilling this need.